mips64 elf64 reloc data structures

[Roland McGrath]

> Even though the standard elf64 relocation data structures work for
> big-endian, they don't for little endian, since MIPS ELF64 uses a
> mixed-endian format for relocation types, that enables it to pack 3
> relocations into a single relocation record.  This patch introduces
> support for such relocation data structures, with accessor macros that
> replace the standard ones when compiling glibc for mips, so that we
> can process n64 LE relocations correctly.  Ok?

Sorry, these decls are too crufty to go into elf.h as is.
Please fix the formatting, to begin with.

Does a standard or another system use these Elf64_Mips_* names?  The struct
and union without typedef names do not match the naming conventions used
for the rest of elf.h.

As to the include/elf.h hack, for which glibc sources do you need these
different macro definitions in effect?